1. Adsorption / Active Carbon
Search :
Go!
Active carbon adsorption
Adsorption is a process where a solid is used for removing a soluble substance from the water. In this process active carbon is
the solid. Active carbon is produced specifically so as to achieve a very big internal surface (between 500 - 1500 m2
/g). This
big internal surface makes active carbon ideal for adsorption. Active carbon comes in two variations: Powder Activated Carbon
(PAC) and Granular Activated Carbon (GAC). The GAC version is mostly used in water treatment, it can adsorb the following
soluble substances:
Datasheet Active Carbon
Examples from active carbon in different processes:
l Ground water purification
l The de-chlorination of process water
l Water purification for swimming pools
l The polishing of treated effluent
Process description:
Water is pumped in a column which contains active carbon, this water leaves the column through a draining system. The
activity of an active carbon column depends on the temperature and the nature of the substances. Water goes through the
column constantly, which gives an accumulation of substances in the filter. For that reason the filter needs to be replace
periodically. A used filter can be regenerated in different ways, granular carbon can be regenerated easily by oxidizing the
l Adsorption of organic, non-polar substances such as:
¡ Mineral oil
¡ BTEX
¡ Poly aromatic hydrocarbons (PACs)
¡ (Chloride) phenol
l Adsorption of halogenated substance: I, Br, Cl, H en F
l Odor
l Taste
l Yeasts
l Various fermentation products
l Non-polar substances (Substances which are non soluble in water)
Menu
2. organic matter. The efficiency of the active carbon decreases by 5 - 10% 1). A small part of the active carbon is destroyed
during the regeneration process and must be replaced. If you work with different columns in series, you can assure that you
will not have a total exhaustion of your purification system.
Description of adsorption:
Molecules from gas or liquid phase will be attached in a physical way to a surface, in this case the surface is from the active
carbon. The adsorption process takes place in three steps:
l Macro transport: The movement of organic material through the macro-pore system of the active carbon (macro-pore
>50nm)
l Micro transport: The movement of organic material through the meso -pore and micro-pore system of the active carbon
(micro-pore <2nm; meso-pore 2-50nm)
l Sorption: The physical attachment of organic material on the surface of active carbon in the meso-pores and micro-pores
of the active carbon
The activity level of adsorption is based on the concentration of substance in the water, the temperature and the polarity of
the substance. A polar substance (= a substance which is good soluble in water) cannot or is badly removed by active carbon,
a non-polar substance can be removed totally by active carbon. Every kind of carbon has its own adsorption isotherm (see
figure 1) and in the water treatment business this isotherm is definite by the function of Freundlich.
The function of Freundlich:
x/m = adsorbed substance per gram active carbon
Ce = concentration difference (between before and after)
Kf, n = specific constants
The second curve from active carbon (see figure 2) shows the exhausting of a filter. Normally we place a UV-disinfections unit
after the active carbon column.
What is the difference between adsorption and absorption??
When a substance is attached to a surface is is called adsorption, is this case the substance is attached to the internal surface
of active carbon. When a substance is absorbed in a different medium it is called absorption. When a gas is taken in a solution
it is called absorption.
Figure 1 gives a specific adsorption isotherm for
active carbon. On the horizontal axis you can find
the concentration and on the vertical axis you can
3. find the necessary quantity of carbon. You can use
this kind of figures to optimize you column.
Source figure 1:
http://www.aapspharmscitech.org/scientificjournals/
pharmscitech/volume2issue1/056/manuscript.htm
Figure 2 tells about the exhaustion during usage of
you column. Point C3 the column starts to break
trough and near C4 your column is not purifying
anymore. Between point C3 and C4 you need to
regenerate you column.
Source figure 2: http://www.activated-carbon.com
Factors that influence the performance of active carbon in water:
4. l The type of compound to be removed. Compounds with high molecular weight and low solubility are better absorbed.
l The concentration of the compound to be removed. The higher the concentration, the higher the carbon consumption.
l Presence of other organic compounds which will compete for the available adsorption sites.
l The pH of the waste stream. For example, acidic compounds are better removed at lower pH.
According to this we can classify some chemicals by their probability of being efficiently adsorbed by active carbon in water:
1.- Chemicals with very high probability of being adsorbed by active carbon:
2.- Chemicals with high probability of being adsorbed by active carbon:
2,4-D Deisopropyltatrazine Linuron
Alachlor Desethylatrazine Malathion
Aldrin Demeton-O MCPA
Anthracene Di-n-butylphthalate Mecoprop
Atrazine 1,2-Dichlorobenzene Metazachlor
Azinphos-ethyl 1,3-Dichlorobenzene 2-Methyl benzenamine
Bentazone 1,4-Dichlorobenzene Methyl naphthalene
Biphenil 2,4-Dichlorocresol 2-Methylbutane
2,2-Bipyridine 2,5-Dichlorophenol Monuron
Bis(2-Ethylhexyl)Phthalate 3,6-Dichlorophenol Napthalene
Bromacil 2,4-Dichlorophenoxy Nitrobenzene
Bromodichloromethane Dieldrin m-Nitrophenol
p-Bromophenol Diethylphthalate o-Nitrophenol
Butylbenzene 2,4-Dinitrocresol p-Nitrophenol
Calcium Hypochloryte 2,4-Dinitrotoluene Ozone
Carbofuran 2,6-Dinitrotoluene Parathion
Chlorine Diuron Pentachlorophenol
Chlorine dioxide Endosulfan Propazine
Chlorobenzene Endrin Simazine
4-Chloro-2-nitrotoluene Ethylbenzene Terbutryn
2-Chlorophenol Hezachlorobenzene Tetrachloroethylene
Chlorotoluene Hezachlorobutadiene Triclopyr
Chrysene Hexane 1,3,5-Trimethylbenzene
m-Cresol Isodrin m-Xylene
Cyanazine Isooctane o-Xylene
Cyclohexane Isoproturon p-Xylene
DDT Lindane 2,4-Xylenol
Aniline Dibromo-3-chloropropane 1-Pentanol
5. 3.- Chemicals with moderate probability of being adsorbed by active carbon*:
*(For this chemicals active carbon is only effective in certain cases).
4.- Chemicals for which adsorption with active carbon is unlikely to be effective. However it may be viable in certain cases
such as for low flow or concentrations:
Factors that influence the performance of active carbon in air:
l Type of compound to be removed: In general compounds with a high molecular weight, lower vapor pressure/higher
boiling point and high refractive index are better adsorbed.
l Concentration: The higher the concentration, the higher the carbon consumption.
Benzene Dibromochloromethane Phenol
Benzyl alcohol 1,1-Dichloroethylene Phenylalanine
Benzoic acid cis-1,2- Dichloroethylene o-Phthalic acid
Bis(2-chloroethyl) ether trans-1,2- Dichloroethylene Styrene
Bromodichloromethane 1,2-Dichloropropane 1,1,2,2-Tetrachloroethane
Bromoform Ethylene Toluene
Carbon tetrachloride Hydroquinone 1,1,1-Trichloroethane
1-Chloropropane Methyl Isobutyl Ketone Trichloroethylene
Chlorotoluron 4-Methylbenzenamine Vinyl acetate
Acetic acid Dimethoate Methionine
Acrylamide Ethyl acetate Methyl-tert-butyl ether
Chloroethane Ethyl ether Methyl ethyl ketone
Chloroform Freon 11 Pyridine
1,1-Dichloroethane Freon 113 1,1,2-Trichloroethane
1,2-Dichloroethane Freon 12 Vinyl chloride
1,3-Dichloropropene Glyphosate
Dikegulac Imazypur
Acetone Methylene chloride
Acetonitrile 1-Propanol
Acrylonitrile Propionitrile
Dimethylformaldehyde Propylene
1,4-Dioxane Tetrahydrofuran
Isopropyl alcohol Urea
Methyl chloride
